The invention relates to a method for producing a particularly dimensionally stable cable set or assembly, as well as a foaming tool for realizing this method.
A dimensionally stable cable set (DSC) generally refers to a cable set, meaning a bundle of single conductors, which cable set has a predetermined geometry and is dimensionally stable. In order to produce the dimensionally stable cable set, the single conductors are generally inserted into a special mold, the so-called foaming tool. A foaming material, which is initially in a liquid state, is subsequently poured around these conductors. Polyurethane (PU) foam is preferably used for this. A dimensionally stable cable set of this type is used especially in motor-vehicle engineering and functions as a prefabricated structural unit for running electrical lines inside the motor vehicle. The geometric boundary conditions predetermined by the motor vehicle construction, meaning the space conditions and the predetermined paths for the cable set, are taken into consideration when producing the set as a dimensionally stable unit.
As a result of the generated foam, pressure forces are exerted onto the foaming tool. The foaming tool therefore must exert a counter pressure in order to impress the shape, predetermined by the foaming tool, onto the cable set and to prevent the foam from flowing out of the mold. For that reason, traditional foaming tools have respectively a solid bottom half and top half that are pressed together with the aid of involved hydraulic equipment. Due to the high forces that the foaming tool must withstand, the top half and the bottom half must be designed to be extremely solid and of heavy construction.
The object of the invention is to make possible a simple production of a particularly dimensionally stable cable set.
According to the invention, the above object generally is solved with a method for producing a particularly dimensionally stable cable set, having a number of single conductors that are inserted into the cavity of a foaming tool. The foaming tool comprises a top half and a bottom half between which the single conductors are inserted. A vacuum is generated between the top half and the bottom half and a foaming material injected into the cavity, so that foam surrounds the single conductors.
This embodiment is based on the idea of using low pressure (a vacuum) to press the two foaming tool halves against each other instead of using outside pressure forces. One decisive advantage of this method is that the expensive and involved hydraulic equipment can be dispensed with and that the foaming tool clearly has a lighter and simpler design. In particular, it is possible to use a plastic tool in place of the metal tool, required so far, or to produce at least one of the two halves from plastic.
The vacuum preferably is adjusted inside the cavity. According to one preferred modification, the space beside the cavity, between the two halves, is additionally or alternatively provided with a vacuum. A vacuum space is provided for this, inside of which the vacuum can be generated. As a result, the regions of the upper half and the lower half that flank the cavity are also pressed together firmly.
The vacuum space is preferably provided in the form of vacuum channels that extend along the cavity, so that the tool halves (upper half and lower half) are pressed securely and firmly against each other along the cavity, which generally has a long stretched-out shape.
Based on one useful modification, different vacuum levels are adjusted in the cavity and the vacuum space, wherein a lower pressure is adjusted in the cavity, in particular, than in the vacuum space. As a result, the cavity retains its desired shape and is not deformed, for example due to an excessively high vacuum. At the same time, it is possible to adjust an extremely high vacuum inside the vacuum space, which ensures that the tool halves are securely pressed against each other and fit tightly against each other. The so-called flashes are thus for the most part avoided. These flashes form because a certain amount of the foaming material is pressed during the foaming operation into the sealing surface between the tool halves. Flashes of this type, which are also called filmy skins, generally must be removed later on with costly and involved reworking operations.
For the same reason, namely to prevent the development of flashes, different vacuums are preferably adjusted in various partial areas of the vacuum space. The vacuum space is thus divided into different partial areas. The vacuum values can be adjusted independent of each other, meaning optionally, in the partial vacuum spaces, as well as in the cavity itself. The essential advantage of having separate partial spaces is that a higher vacuum can specifically be adjusted in regions where flashes occur, so that the forces for pressing together the tool halves can be increased. Thus, the contact pressure forces between the top half and the bottom half are increased in those areas where flashes occur. The vacuum channels extending along both sides of the cavity represent partial spaces of this type. If different vacuums are adjusted in these vacuum channels, then the two tool halves are pushed together more on one side than on the other. This results in a so-to-speak slight xe2x80x9ctiltingxe2x80x9d of the upper half relative to the lower half, away from the parallel alignment.
It is advantageous if the vacuum inside the cavity is monitored during the filling of the foaming tool to prevent a deformation of the cavity, as well as the formation of air bubbles. In particular, no vacuum or only a slight vacuum is adjusted in the cavity at the start of the process, meaning when the foaming material is initially introduced. With increasing foam formation, the foam displaces the air trapped inside the cavity and there is danger that air bubbles will form. In that case, the pressure inside the cavity is monitored during the process and, for example, is maintained at a specific value. The air that is condensed as a result of the foaming is drawn off, so-to-speak, to prevent the forming of air bubbles.
According to another preferred embodiment, an opening in the foaming tool toward the cavity is automatically closed once a specific pressure value inside the cavity is exceeded, so as to prevent foam from leaking out.
The object is furthermore solved according to the invention with a foaming tool for a particularly dimensionally stable cable set. The foaming tool comprises a bottom half and a top half that form a cavity for inserting a number of single conductors for the cable set when they are pressed together, wherein a vacuum can be generated between the bottom half and the top half.
The preferred embodiments and advantages listed for this method must also be transferred by analogy to the foaming tool.
According to one preferred modification, the foaming tool is provided with a number of adjacent vacuum channels. As a result, both tool halves are pressed together over a comparably large area. Owing to the fact that each of the vacuum channels additionally has a quasi-sealing function, a type of sealing cascade is obtained if several vacuum channels are arranged next to each other.
To obtain the best possible seal, it is advantageous if the top half and the bottom half interlock in accordance with the tongue-and-groove principle. A number of adjacent tongue-and-groove seals are preferably provided for this.
For the same purpose of obtaining a better seal, a sealing element is preferably provided between the upper half and the lower half, directly bordering the cavity area. This sealing element in particular is designed as a separate element and preferably consists of a special sealing material such as rubber.
Additional preferred embodiments of the foaming tool follow from the dependent claims.
Exemplary embodiments of the invention and additional modified designs of the foaming tool are explained in further detail in the following with the aid of Figures, which show respectively in schematic representations: